PowerPoint Slideshow about 'Introduction to Web Services' - lewis

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

A resource is never cached and is always downloaded; even with back/forward buttons.

A resource can be cached but has no expiration or modification date. In this case it is always downloaded when the page is first visited in a new browser session or if the user refreshes the page.

A resource can be cached and has a modification date but no expiration date. Therefore it is always checked but not downloaded when the page is first visited in a browser session or if the user refreshes the page.

A resource can can be cached and has an expiration date. The browser can reuse the image in a new browser session without having to send any request to the server.

For example, the Google logo is set to expire in 2038 and will only be downloaded on your first visit to google.com or if you have emptied your browser cache. To change the image they can use a different image file name or path.

The HTTP method (sometimes called ‘verb’) is supplied in the request and specifies the operation that the client has requested.

There are lot of methods defined (GET, POST, HEAD, OPTION, DELETE, PUT, …) but the most used are GET and POST

The GET method is used to retrieve information from a specified URI

It is the typical method used to display a web page in a browser

The GET method has only a header. There is no body.

GET requests can only supply data in the form of parameters encoded in the URI (known as a Query String) or as cookies in the cookie request header.

The POST method has a body in addition to the header that can be used to transfer information

The POST content body that is normally used to send parameters and data. Unlike using the request URI or cookies, there is no upper limit on the amount of data that can be sent and POST must be used if files or other variable length data has to be sent to the server.

For normal text (not markup), there are no special characters: just make sure your document refers to the correct encoding scheme for the language and/or writing system you want to use, and that your computer correctly stores the file using that encoding scheme.

In all cases you can use a symbolic notation called ‘entity referencing’. Entity references can either be numeric, using the decimal or hexadecimal Unicode code point for the character

Example: if your keyboard has no Euro symbol (€) you can type &#8364;

You can also have “short names” which you declare in your DTD (eg <!ENTITY euro "&#8364;">) and then use as &euro; in your document.

If you are using a Schema, you must use the numeric form for all except the five below because Schemas have no way to make character entity declarations.

If you use XML with no DTD, then these five character entities are assumed to be predeclared, and you can use them without declaring them:

Discussed later

Entity references always start with the "&" character and end with the ";" character.

Note: Only the characters "<" and "&" are strictly illegal in XML. Apostrophes, quotation marks and greater than signs are legal, but it is a good habit to replace them.

XML allows developers to create their own XML vocabularies that are customized for describing their particular data structures.

Once developers harness the power of XML to describe their data, they can easily interoperate with any other homogenous or heterogeneous system that also understands XML.

Developers can consume data from any other system as long as it's also described using XML. A developer who leverages XML no longer needs to worry about platform, operating system, language, or data store differences when interoperating with other systems.

Because XML is truly about interoperability and everyone is free to create their own XML vocabularies, everything would start to break down rather quickly if different developers chose identical element names to represent conceptually distinct entities.

To safeguard against these potential conflicts, the W3C introduced namespaces into the XML language.

“Definition: A Web service is a software system identified by a URI [RFC 2396], whose public interfaces and bindings are defined and described using XML. Its definition can be discovered by other software systems. These systems may then interact with the Web service in a manner prescribed by its definition, using XML based messages conveyed by Internet protocols.”

“It's remote procedure calling using HTTP as the transport and XML as the encoding. XML-RPC is designed to be as simple as possible, while allowing complex data structures to be transmitted, processed and returned.”

“We wanted a clean, extensible format that's very simple. It should be possible for an HTML coder to be able to look at a file containing an XML-RPC procedure call, understand what it's doing, and be able to modify it and have it work on the first or second try. “

Easy to implement

“We also wanted it to be an easy to implement protocol that could quickly be adapted to run in other environments or on other operating systems.”

An accessor "...that can polymorphically access values of several types, each type being available at run time. A polymorphic accessor instance MUST contain an "xsi:type" attribute that describes the type of the actual value."

Describes the abstract interface of a web service and the details how a specific web service has implemented it

“WSDL defines an XML grammar for describing network services as collections of communication endpoints capable of exchanging messages. WSDL service definitions provide documentation for distributed systems and serve as a recipe for automating the details involved in applications communication.”